Two hands clap and there is a sound. What is the sound of one hand?
— Hakuin Ekaku
Two hands clap and there is a sound. What is the sound of one hand?
— Hakuin
Ekaku
When two people push or pull against each other but neither one moves, we rationalized that they were both exerting the same force, just in opposite directions. Can an object exert a force against a person??
Every force is an interaction between two objects.
Whenever one body exerts a force on a second body, the second exerts a force on the first.
Furthermore, the two forces are
Can
be thought of getting into a position (leaning and turning), where
you're manipulating the earth into pushing you.
Typical air resistance at highway speeds: several hundred pounds.
Two strategies to reduce this....
Driving half
the speed cuts the force down by a factor of 4 (one quarter).
Speed limits were dropped 75 mph -> 55 mph in the aftermath of the Arab oil crisis in the 1970s.
Arranging the surfaces so they're at a shallow angle to the
air stream.More important the faster you're going (see "Drive slower").
Airplanes stay in the air by moving forward, and angling their wings to push air down. The reaction force causes them to go up.
The effective "gas mileage per passenger" for airline travel is ~30 mpg for each passenger.
Could airlines save money / fuel by re-designing planes to fly slower, just like automobiles?
Unfortunately, the answer is no: The slower a plane goes, the greater the wing area needed to push down enough air to keep it aloft. This increased air resistance pretty closely compensates for the slower speed, and there's no net savings.
without air to push against?
Bring
your own stuff* to push against.
*Rocket fuel is both the 'stuff' that the rocket pushes against, as well as the source of energy for doing the pushing.
If a bug hits my windshield, or rather, if my car windshield hits a
bug...Is the force that the car exerts on the bug really equal to the force
that the bug exerts on my car?
Forces acting on a cyclist include
Conceptual Exercises in Chapter 4: 10, 11, 21.
Problems in Chapter 4: 17, 18.
3fold, Stilleben mit offener Schublade by Paul Cezanne, Robert Scoble, Max, Richard Masoner, Graham Watson, Constihill, Colin, RGT3, Amblin, Tyler Durdin
